Research is being conducted on how lac operator DNA interacts with lac repressor protein. The approach is to chemically synthesize lac operator DNA and modified operator DNA, followed by studies on how these DNAs interact with repressor protein. Several deoxyoligonucleotides have been made (Federation Proceedings Abstracts 34, 1891, 1975). Recent work involves synthesis of deoxyoligonucleotides with modified sequences or with 5-bromodeoxyuridine inserted at specific sites for thymidine. Research in progress involves studies on how modified operators interact with repressor protein, attempts to purify operator cross-linked with repressor protein from starting materials, and fluorescence changes in repressor protein during binding to operator DNA.